The primary objectives of the proposal are: 1) To develop an objective Behavior Observation Scale (BOS) which will differentiate autistic from normal and mentally retarded children (30-60 months of age); 2) To differentiate subgroups of autistic children along various symptom axes; 3) To establish a quantitative continuum of severity within each symptom subgroup; 4) To generate computer determined objective diagnostic profiles along developmental parameters; 5) To conduct a prospective longitudinal study which periodically re-evaluates the children in order to generate diagnostic norms for autism and trace the natural course of the syndrome. In order to accomplish these objectives, normal, autistic and retarded children will be observed a structured setting and their behaviors counted on the Behavior Observation Scale (BOS). Data obtained on the BOS will be subjected to a discriminant analysis which will: 1) Differentiate among groups of children; 2) Divide children according to symptom subclusters and 3) Provide a quantitative continuum of severity in each subcluster. These data will be correlated with data obtained from developmental history, psychiatric interviews, clinical, psychometric and language evaluations and diagnostic profiles generated. Age and mental age norms will be developed for all parameters by conducting systematic periodic re-evaluations of all children.